1. Field of the Invention
The present invention relates to a magnetoresistive element, a magnetic random access memory and a method of manufacturing them.
2. Description of Related Art
A magnetic random access memory (MRAM) has been expected as a nonvolatile memory capable of performing rewriting an infinite number of times with a high speed and actively developed. The MRAM uses a magnetoresistive element as a memory cell. An example of the magnetoresistive element is a TMR (Tunneling Magneto Resistive) element having magnetic tunneling junction (MTJ). The MTJ is composed of a free layer whose magnetization can be switched, a pinned layer whose magnetization is pinned, and a barrier layer provided between the pin layer and the free layer. The magnetoresistive element stores data as a magnetization direction of the free layer.
As a method of manufacturing of the magnetoresistive element, for example, Japanese Patent Publication JP2004-179250β discloses a method of manufacturing a magnetic tunneling junction element and a magnetic tunneling junction device. FIGS. 1 and 2 are sectional views showing the method of manufacturing the magnetic tunneling junction element described in JP2004-179250A. According to the method of manufacturing the magnetic tunneling junction element, first, a laminated layer including a first conductive material layer 124, a antiferromagnetic layer 126, a first ferromagnetic layer 128, a tunnel barrier layer 130, a second ferromagnetic layer 132 and a second conductive material layer 134 from the bottom is formed on an insulating film 122 which covers a substrate 120. Next, the second conductive material layer 134 is selectively etched using a resist layer 136 to form a first hard mask 134 (FIG. 1). Subsequently, the laminated layer is etched up to the antiferromagnetic layer 126 by ion milling using the first hard mask 134 as a selection mask to form a separation groove 138 (FIG. 2). At this time, a deposit DP adheres to a side surface of a magnetic tunnel junction part AT, namely, a side wall of the groove 138. Thus, the deposit DP adhering to the side wall of the groove 138 is removed by chemical treatment and then, the side wall is protected with a second hard mask made of an insulating material, and further, the separation groove is made deeper by ion milling to obtain the magnetic tunneling junction element.
As another method of manufacturing the magnetoresistive element, for example, Japanese Patent Publication JP2004-214600A (corresponding US Patent application: US2004127054 (A1)) discloses a method of forming a magnetic RAM. FIGS. 3 and 4 are sectional views showing the method of forming the magnetic RAM described in JP2004-214600A. According to the method of forming the magnetic RAM, first, a connecting metal layer 143 connected to a semiconductor substrate via a lower insulating layer 141 is formed. Next, a pinned magnetization layer 145, a tunnel barrier layer 147 and a free magnetization layer 149 are laminated on the connecting metal layer 143. Subsequently, a hard mask layer 151 is formed on the free magnetization layer 149. Then, the hard mask layer 151 and the free magnetization layer 149 are etched in a photolithographic etching step using an MTJ cell mask to make the tunnel barrier layer 147 exposed. Subsequently, a blocking layer 155 and an insulating film 157 are sequentially formed on the whole surface. Then, the insulating film 157 is anisotropically etched to form an insulating film spacer 157 on side walls of the hard mask layer 151 and the free magnetization layer 149 (FIG. 3). After that, using the insulating film spacer 157 and the hard mask layer 151 as masks, the tunnel barrier layer 147, the fixed magnetization layer 145 and the connecting metal layer 143 are etched to form the MTJ cell and the connecting layer 143 (FIG. 4).
We have now discovered the following facts.
As described above, according to the method described in JP2004-179250A, when the separation groove 138 is formed by ion milling (FIG. 2), the conductive deposit DP adheres to the side surface of the magnetic tunnel junction part AT, namely, the side surface of the barrier layer (tunnel barrier layer 130). For this reason, a short-circuit occurs between the upper magnetic layer (second ferromagnetic layer 132) and the lower magnetic layer (first ferromagnetic layer 128). In order to avoid the short-circuit, this method requires the step of removing the deposit DP by chemical treatment. In addition, in order to prevent adhesion of the deposit by subsequent ion milling, it is need to form a second hard mask for protecting the side surface of the magnetic tunnel junction part AT and perform additional ion milling.
According to the method described in JP2004-214600A, the above-mentioned adhesion of the deposit to a side surface of a barrier layer can be prevented. That is, first, only the upper magnetic layer (free magnetization layer 147) is etched and shaped and then, its side surface is covered with the blocking layer 155 and the insulating film spacer 157 (FIG. 3). After that, the barrier layer (tunnel barrier layer 147) and the lower magnetic layer (pinned magnetization layer 145) are separately shaped by etching to form the MTJ cell (FIG. 4). Thus, even when the deposit adheres to the side surface of the barrier layer, the blocking layer 155 and the insulating film spacer 157 prevent the short-circuit from occurring between the upper magnetic layer and the lower magnetic layer. However, according to this method, the barrier layer needs to be used as a stopper layer in etching. The barrier layer is generally a very thin film having a thickness of a few nm. For this reason, when a plurality of magnetoresistive elements are manufactured, for example, for MRAM, it may not easy to stop etching at an upper surface of the barrier layer in all of the magnetoresistive elements. As a result, manufacturing yield may lower.